how to redirect www.mysite.com to https://mysite.com in DNS records or apache2 ?

Using a rewrite in an .htaccess file you could do it with:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

or you could create a separate VirtualHost file for www and redirect it from there like this:

<VirtualHost *:80>
        ServerName www.example.com
        Redirect permanent / http://example.com/
</VirtualHost>